There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

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The HITRAN 2008 molecular spectroscopic database

Feshbach resonances are the essential tool to control the interaction between atoms in ultracold quantum gases. They have found numerous experimental applications, opening up the way to important breakthroughs. This review broadly covers the phenomenon of Feshbach resonances in ultracold gases and their main applications. This includes the theoretical background and models for the description of Feshbach resonances, the experimental methods to find and characterize the resonances, a discussion of the main properties of resonances in various atomic species and mixed atomic species systems, and an overview of key experiments with atomic Bose-Einstein condensates, degenerate Fermi gases, and ultracold molecules.

Feshbach resonances in ultracold gases

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

/pdf/proton-coupled-electron-transfer-3oyvp0w9qd.pdf

Proton-Coupled Electron Transfer

A self-consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1-18, Z=1-118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E-E, E-H, and E-CH 3 data are incorporated for most elements, E. Many E-E' data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl-based one of Suresh and Koga [J. Phys. Chem. A 2001, 105, 5940] and its predecessors. For the diatomic alkalis MM' and halides XX', separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition-metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H 2 and F 2 . The standard deviation for the 410 included data points is 2.8 pm.

Molecular single-bond covalent radii for elements 1-118.

This paper describes program LEVEL, which can solve the radial or one-dimensional Schrodinger equation and automatically locate either all of, or a selected number of, the bound and/or quasibound levels of any smooth single- or double-minimum potential, and calculate inertial rotation and centrifugal distortion constants and various expectation values for those levels. It can also calculate Franck–Condon factors and other off-diagonal matrix elements, either between levels of a single potential or between levels of two different potentials. The potential energy function may be defined by any one of a number of analytic functions, or by a set of input potential function values which the code will interpolate over and extrapolate beyond to span the desired range.

/pdf/level-a-computer-program-for-solving-the-radial-schrodinger-b1m45q5fun.pdf

LEVEL: A computer program for solving the radial Schrödinger equation for bound and quasibound levels

Two types of combined-isotopologue analysis have been performed on an extensive spectroscopic data set for ground-state N2 involving levels up to v=19, which is bound by half the well depth. Both a conventional Dunham-type analysis and a direct-potential-fit (DPF) analysis represent the data within (on average) the estimated experimental uncertainties. However, the Dunham-type parameters do not yield realistic predictions outside the range of the data used in the analysis, while the potential function obtained from the DPF treatment yields quantum mechanical accuracy over the data region and realistic predictions of the energies and properties of unobserved higher vibrational levels. Our DPF analysis also introduces a compact new analytic potential function form which incorporates the two leading inverse-power terms in the long-range potential.

An accurate analytic potential function for ground-state N2 from a direct-potential-fit analysis of spectroscopic data.

A method is developed for analyzing the discrete infrared absorption spectra of the van der Waals complexes formed between H2 or D2 and Xe, Kr, Ar, or Ne. Its application involves automatic nonlinear least squares fits of trial spectra calculated from realistic three‐dimensional intermolecular potential models, to the experimental data. The secular determinant method used for calculating the energy levels of the anisotropic trial potentials proves to be highly reliable and relatively inexpensive. As a result, the present techniques should be readily applicable to cases where the anisotropic part of the potential is much stronger than it is here. The potential form used here is a Lennard‐Jones (m, 6) function with independent long‐ and short‐range anisotropy coefficients, and independent parameters characterizing the effect of the stretching of the hydrogen bond on the attractive and repulsive parts of the potential. The final fits concurrently used all uniquely assigned and nonoverlapping lines of both isotopes (H2 and D2) of a given complex, and all parameters (except ``m,'' which was varied manually) were allowed to vary simultaneously. The resulting potential surfaces are compared with those determined from molecular beam and relaxation time measurements.

Anisotropic intermolecular potentials from an analysis of spectra of H2‐ and D2‐inert gas complexes

A combined analysis of discrete infrared and microwave spectra, elastic and inelastic differential cross section measurements, and virial coefficient data has been used to determine improved potential energy surfaces for the H2–Ar, –Kr, and –Xe systems. Key improvements over previous surfaces for these species are an improved delineation of the diatom bond length dependence of the potential anisotropy, and the first experimental determination of a distinct P4(cos θ) anisotropy for an atom–diatom system. The effective anisotropy strength seen by bound state properties (such as transition frequencies) is found to increase from H2–Ar to H2–Kr to H2–Xe, although that seen by properties sensitive to the short‐range potential (such as rotational predissociation and rotational inelasticity) decreases along this series. This reflects the lack of conformality of the various potentials; however, both these and analogous trends predicted for properties such as vibrational frequency shifts and vibrational inelasticit...

Improved potential energy surfaces for the interaction of H2 with Ar, Kr, and Xe

http://scienide2.uwaterloo.ca/~rleroy/Pubn/87JMS-SchwartzH2.pdf

Robert J. Le Roy

Papers

LEVEL: A computer program for solving the radial Schrödinger equation for bound and quasibound levels

An accurate analytic potential function for ground-state N2 from a direct-potential-fit analysis of spectroscopic data.

Anisotropic intermolecular potentials from an analysis of spectra of H2‐ and D2‐inert gas complexes

Improved potential energy surfaces for the interaction of H2 with Ar, Kr, and Xe

Nonadiabatic eigenvalues and adiabatic matrix elements for all isotopes of diatomic hydrogen